KARE11 viewer, Scharre Gerrety, sent several photos after seeing what resembled ice chunks floating in the water.

After a quick trip to the water, KARE11 verified that ice wasn't the culprit. It was actually a thick foam.

"Not good," said Pat Murphy, who has enjoyed visiting the Mississippi River for more than 40 years. "I've seen something like this before, but not often. I think it looks like a foam from a soap or a detergent, but that it has too much resilience."

KARE 11 reached out to the US Army Corps of Engineers in search of answers. Lockmaster Mike DeRusha, says the foam forms and builds up as it travels between Upper and Lower St Anthony Falls Lock and Dam. He says it usually isn't enough to turn heads.

"It's usually only about 3 or 4 times a year you'll actually see it," DeRusha said.

On those days, he says a combination of water and air temperature cause the foam to really pile up before passing over the falls.

"When it gets somewhere where there's an obstruction, it starts building up just like snow drifts do," he said. "I'm going to say 8-10 feet high."

But even at that height, he says it's not a major environmental concern.

"People think it's a pollutant, and it's not." DeRusha said. "When I first saw it, years ago, I actually made sure it was tested from the EPA and we found out it's all biological. Basically, what they said is it's tannins and the breakdown of some of the material from up river."

The director of the University of Minnesota Water Resources Center, Jeffrey Peterson explained it in greater detail:

"It is quite common to have foam on water bodies in the autumn. It often the result of the die-off and decay of aquatic plants, whose cells release their natural oils as they decompose."

Though it is also possible for contaminant spills (detergents, oils) to create foam in waterways, KARE 11 could not find any documented spills that would have led to the type, and scope, of foam witnessed on Wednesday.